Allow easy creation of complex-coefficient systems using e.g., ss?

[olof3]

Should it for example be allowed to create StateSpace objects using the convenience constructor ss?

Very few users want to use complex-valued linear systems, and will most likely only create them by mistake, leading to confusion.

Some options:

• Only allow it for the actual constructor StateSpace{Matrix{Complex128}, Complex128}
• Allow it
• Allow it, but issue a warning (Matlab does this for example)
• Some other mechanism

I guess one should also consider (the future possibility) of creating symbolic systems. Any thoughts?

[mfalt]

I think that if the elements of the matrices (either A,B,C,D) are complex, there is little reason to throw an error at the user. I say either Allow it or Allow with warning.